Movie Idea: New in town

There is a group of friends (or workers, or members of a team) that have been together for years. They know exactly how everyone will act at all times. Then someone new shows up- maybe from another school, another team, or something completely unrelated to the original group. The new person starts changing the way the group works. The group is starting to fall apart, right when a major crisis calls for them to work together. What happens?